Electrical instrument in which string serves as its own transducer



J. c. COOKERLY ET AL 3,297,813 ELECTRICAL INSTRUMENT IN WHICH STRING SERVES Jan. 10, 1967 AS ITS OWN TRANSDUCER Filed Dec. 13, 1962 2 Sheets-Sheet 1 S y MT W M ma KR mm JG Y B a. 9 3 M\ 8 1/ m $5. M U. /5 3 M.

FIG. 2

Jan. 10, 1967 q COOKERLY ET AL 3,297,813

ELECTRICAL INSTRUMENT IN WHICH STRING SERVES AS ITS OWN TRANSDUCER 2 Sheets-Sheet 2 Filed Dec. 13, 1962 FIG. 4

, INVENTORS JACK c. COOKERLY GEORGE R. HALL ATTORNEYS United States Patent 3,297,813 ELECTRICAL INSTRUMENT IN WHICH STRING SERVES AS ITS OWN TRANSDUCER Jack C. Cookerly, 7655 Atoll Ave., North Hollywood,

Calif. 90028, and George R. Hall, 13613 Huston Sh,

Sherman Oaks, Calif. 91403 Filed Dec. 13, 1962, Ser. No. 244,376 4 Claims. (Cl. 841.16)

This invention relates generally to electrical instruments and more particularly to stringed instruments in which an electrical signal is generated in response to string vibrations for reproduction through a loud speaker.

An example of the type of electrical instrument with which the present invention deals is the electric guitar and for purposes of illustrating certain embodiments of the invention, its use in conjunction with an electric guitar will be described. It should be understood, however, that the invention may be applied to other analogous stringed instruments.

Conventional electric guitars incorporate some type of transducer means for generating an electrical signal in response to vibration of the strings. Basically, two types of transducers are possible: first, an electrostatic transducer wherein a change in capacity, for example, can be effected in response to physical string vibrations, and this resulting change in capacity electrically detected to provide the desired output signal. Second, electromagnetic means wherein one or more coils with magnetic cores are employed in conjunction with a string of ferrous material which varies the coil field when vibrating in such a manner that the desired output signal is generated in the coil.

The electrostatic transducer system is necessarily a high impedance device and, therefore, introduces a serious shielding problem in order to eliminate hum. In addition, there is usually required a high D.-C. polarizing voltage which also necessitates shielding for practical purposes.

The electromagnetic type of pick-up employing a coil overcomes the objection of high impedance, but it is very difiicult to design in such a manner as to eliminate pickup from adjacent strings on the instrument. This latter problem can become very serious in electrical instruments of the type such as described in our co-pending patent application Serial No. 153,467, filed November 20, 1961, now Patent No. 3,213,180, for Tone Generation System, wherein the output from each individual string is fed into a trigger circuit to provide signals of double or half frequencies or of particular wave shapes. Such trigger circuits are sensitive and if there is not proper isolation between the various strings, one may serve to trigger the circuit associated with an adjacent string.

In addition to the above, in many present day transducer systems, the transduced signal is different when the string is plucked towards rather than away from the pickup. This lack of symmetry diminishes the fidelity of the system.

Other problems relate to undesirable resonances generated in the body portion of the instrument upon which the strings are mounted. With presently available transducing systems, such undesirable resonant conditions are detected along with the desired string movements from the artists playing of the strings. It would be highly advantageous to incorporate in a transducer system means for minimizing or eliminating such undesirable resonant conditions.

To avoid general bulkiness, present day transducer systems of both the electrostatic and electromagnetic type are miniaturized as much as possible. As a consequence, only a very small portion of the string is em- 3,297,813 Patented Jan. 10, 1967 ployed to provide the movement to be transduced. As a result, traveling harmonics in the string tend to be accentuated. Stated differently, when only a small portion of the string is employed, any traveling harmonic constitutes a relatively large percentage of the string movement that is transduced. Further, the sustaining power of the string in present day transducer systems is somewhat limited. Thus, even though the string may still be vibrating, the sound appears to drop off relatively quickly rather than be sustained as is the case when the instrument is employed as a conventional sound instrument.

With all of the foregoing in mind, it is a primary object of the present invention to provide a greatly improved electrical instrument incorporating novel transducer means in which the foregoing problems are substantially eliminated.

More particularly, it is an object to provide in an electrical instrument a low impedance transducer means to the end that shielding may be substantially eliminated.

Another object is to provide a low impedance transducer for a stringed instrument in which pickup from adjacent strings is substantially eliminated.

Another important object of this invention is to provide a transducer which may be polarized to the extent that undesirable resonances resulting from vibrations in the strings in given planes are automatically eliminated.

Another object is to provide a transducer which provides similar signals whether the string is plucked forwardly or backwardly.

Another object is to provide an improved transducer for a stringed instrument which is compact, simple in construction, and avoids any bulky structure which might otherwise interfere with an artists attack on the strings.

Still another object is to provide a transducer in which the percentage content of traveling harmonics is greatly reduced and which has a relatively long sustaining power as compared to transducers presently available.

Briefly, these and many other objects and advantages of this invention are attained by avoiding the use of any type of electrostatic transducer or coils in a magnetic type transducer. Rather, a transducer employing magnetic principles is used, but rather than coils, there is simply provided a relatively uniform magnetic field in a given direction for each string in question. Vibration of the strings themselves through the magnetic fields respectively will then induce currents in the strings and each individual string serves as its own transducer. Individual pickup means are then connected to opposite ends of the strings, respectively, and passed through any suitable impedance matching means and individual amplifiers so that the induced currents in the strings themselves are properly matched and amplified to provide the desired output signals.

In the preferred embodiment of the invention, the magnetic fields are provided by a magnetic material in the form of an elongated, fiat, rectangular member having elongated strip portions thereof magnetized so that opposite sides constitute north and south poles. The member itself may be relatively thin so that it will easily fit beneath the strings of the guitar without interference therewith. Further, by making the member relatively long, a substantial portion of each string will lie in its associated magnetic field so that the fundamental signal induced at any one instance is large compared to any traveling harmonic along the string. Moreover, a desired sustaining power is realized.

As a consequence of the use of individual pickups for each of the strings, there is substantially no interference from adjacent strings so that excellent isolation between the individual strings is realized. In addition, by directing the magnetic fields in given directions, only movement of the string in planes cutting across or forming an angle to this direction will result in the inducing of current in the string so that vibrations in undesirable planes as might result from resonances, for example, will have substantially no effect on the output signal.

In a second embodiment of the invention, the strings are connected in series so that only a single output circuit is necessary. While isolation is not realized to the extent in the first embodiment, a more economical instrument is provided.

A better understanding of the invention will be had by now referring to the preferred embodiments thereof as illustrated in the accompanying drawings, in which:

FIGURE 1 is a plan view partly schematic in form illustrating a musical instrument incorporating the preferred embodiment of the present invention;

FIGURE 2 is an enlarged schematic perspective view illustrating one of the components of the instrument in FIGURE 1;

FIGURE 3 is an enlarged fragmentary cross section in the direction of the arrows 3-3 of FIGURE 2; and,

FIGURE 4 is a fragmentary schematic plan view of a second embodiment of the invention.

Referring to FIGURE 1, there is shown a musical instrument in the form of an electric guitar including a body portion having an elongated neck 11 extending from one end thereof. As shown, the guitar includes six strings 12, 13, 14, 15, 16, and 17, respectively terminating at first ends in suitable tuning stops 18 and having their other ends pass over a bridge 19 to be secured to the body 10. The instrument described thus far is entirely conventional with the exception of the neck 11.

In accordance with the invention, the neck incorporates a novel transducer means in the form of magnetic material 20 for generating magnetic fields in given directions with respect to the plane of the strings 12-17. The material 20 is disposed between the bridge 19 and the tuning stops 18. While the neck itself preferably is structurally formed at least in part from the magnetic material 20, a separate magnetic member substantially coextensive with and secured to the neck could be provided.

Associated with each of the individual strings are a plurality of pickup means in the form of impedance matching devices such as transformers 21, 22, 23, 24, 25, and 26. As shown, the inputs to these transformers are connected, respectively, across opposite ends of the individual strings 12-17. The outputs from the impedance matching devices, respectively, connect into individual amplifiers 27, 28, 29, 30, 31, and 32. The outputs of each amplifier in turn provides a signal which is a function of the frequency and amplitude of vibration of its associated string.

Referring now to FIGURE 2, there is shown in fragmentary perspective form the magnetic material 20 forming the neck together with portions of the strings 1217 passing thereover. As shown, the material 20 is in the form of a flat elongated rectangular member and may constitute a hard rubber or plastic impregnated with barium ferrite. This member has eight individual portions in the form of strips 33, 34, 35, 36, 37, 38, 39, and 40 individually magnetized to define N and S poles along opposite sides as indicated by the lettering N and S. The center six strips 34-39 lie beneath the six strings 12-17 respectively as shown and provide a magnetic field individual to each string. The end strips 33 and 40 are provided so that the magnetic fields for the outside strings 12 and 17 will be uniform.

Referring to FIGURE 3, the magnetic field represented by the flux lines H will extend generally from one side of the strip 35 to pass over the surface of the strip and close on the opposite side. The positioning of the strings relative to the strips is such that each string is closer to one side than the other so that the magnetic field is at an angle to the plane of all of the strings and vibration of the strings in a transverse or horizontal plane will cause them to cut across the magnetic flux lines H. The extent of the strips is preferably greater than fifty percent of the length of the strings so that a relatively long portion of each of the individual strings will lie in its associated magnetic field.

When the instrument is played, the strings are general- 1y plucked in such a manner that they will vibrate in the direction of the line 41 so that maximum current will be induced in each string since it cuts across the lines of flux H at approximately right angles thereto. However, it is found that the strings will actually vibrate in several planes, this being caused primarily from resonant conditions established by the body 10 and neck 11 illustrated in FIGURE 1. Thus, these supporting body portions have mechanical resonant frequencies which tend to augment the vibrations of the strings genorally in other directions such as along the line 42. Since however, the direction of the line 42 is substantially parallel to the direction of the flux lines, in view of the positioning of the string as shown in FIGURE 3, minimum cutting of flux lines will occur. Therefore,' induced signals in the individual strings resulting from undesirable resonant conditions are minimized.

In the operation of the instrument described in conjunction with FIGURES 1, 2, and 3, it will be evident that downward plucking of the various strings by a right handed artist will result in major vibrations generally in the direction of line 41. Each individual vibrating string which is set in motion will thus cut its associated flux lines H resulting in a current being inducedin the particular string in question. This current will then pass to the particular impedance matching device involved and thence to its associated amplifier illustrated in FIGURE 1 to provide an output signal which has a frequency and amplitude of the vibrating string.

The individual outputs from the various amplifiers would ordinarily be fed into suitable wave shaping circuits, frequency doublers, frequency dividers, or alternatively may connect directly to an audio-amplifier and loud speaker system to reproduce the-original tone. This latter portion of the circuit is not involved in the instant invention, and, therefore, is not shown or described in detail.

As a consequence of the use of individual impedance matching transformers and amplifiers for the individual strings in question, excellent isolation of the various strings is realized. In other words, vibration of adjacent strings will not affect the other strings so that each individual string functions as a unit in and of itself.

FIGURE 4 illustrates a modified embodiment of the invention wherein the feature of isolation is sacrificed in order to reduce the number of components. In this embodiment, there are provided six strings 43, 44, 45, 46, 47 and 48 stretched over a body 49 having a neck 50 incorporating magnetic material 51. The structure thus far described is similar to FIGURE 1. Rather than individual outputs, however, the strings are connected in series as by the jumpers 52, 53, 54, '55, and 56 respectively. A single output transformer 57 is connected to the outside strings 43 and 48 as shown and feeds into a single amplifier 58. By this arrangement, only one output transformer and only one amplifier is required for ail six strings.

It should be noted in both embodiments that as a consequence of making each individual magnetic field relatively uniform, movement of a string in a back and forth direction will result in symmetrical currents being induced therein so that there is not any change in quality as a function of the specific direction of movement of the string in any given plane. I

An additional important advantage of the transducing system of this invention resides in the fact that strings employing ferrous or magnetic material are not neces-' sary. Thus, in many instances, it may be desirable to use copper, brass, nylon or other non-ferrous material for the strings. So long as the material is conductive or rendered conductive by any suitable coating, the instant transducing system will function.

Further, by employing an elongated magnetic field generating means so that a major portion of the string length lies in the magnetic field, the percentage of traveling harmonic sound produced as compared to the fundamental is greatly decreased.

From the foregoing description, it Will be evident that the present invention has provided a greatly improved transducer system for stringed instruments wherein the features of low impedance, avoidance of shielding, harmonic diminution sustaining power, and elimination of undesirable signals resulting from resonant conditions is wholly realized.

While only two particular arrangements for the improved electrical instrument have been shown and described various modifications that fall clearly within the scope and spirit of this invention Will occur to those skilled in the art. The electrical instrument is therefore not to be thought of as limited to the particular embodiments set forth merely for illustrative purposes.

What is claimed is:

1. In a musical instrument including a body and a plurality of strings stretched across a portion of said body, means for providing a plurality of individual magnetic fields in a given direction transverse to said strings; and electrical pickup means for said strings for converting current induced in each string as a consequence of vibrational movement in its associated magnetic field into an electrical signal of magnitude and frequency constituting functions of the magnitude and frequency of vibration of said string, said means for providing a plurality of magnetic fields comprising a fiat elongated rectangular mem ber of magnetic material made up of elongated portions in the form of strips magnetized so that opposite sides constitute north and south poles, said strips being positioned and extending beneath said strings and being of a length greater than fifty percent of the length of said strings.

2. An electrical instrument comprising, in combination: a body having a neck portion extending from one end thereof and terminating in tuning stops; a plurality of strings stretched over said body and secured at first ends to said tuning stops; a bridge secured to said .body; second ends of said strings pasing over said bridge and being secured to said body adjacent to said bridge; a magnetic field generating means comprising an elongated rectangular member of magnetic material incorporated in said neck and having elongated strip portions magnetized so that opposite sides constitute north and south poles, said strip portions being positioned beneath said strings and of a length to extend thereunder over a majority of the length of said strings between said bridge and tuning stops for providing magnetic fields in given directions; a plurality of impedance matching means individually electrically connected to opposite end portions of said strings respectively; and a plurality of individual amplifiers connected to the outputs of said impedance matching means respectively each of said strings including electrically conducting material so that movements of said strings in planes at an angle to said given directions to cut said magnetic fields generates electrical currents in said strings, said currents being amplified by said amplifiers respectively to provide electrical signals constituting functions of the frequencies and amplitudes of said movements of said strings.

3. An instrument according to claim 2, in Which said given directions are oriented in positions substantially parallel to the direction of movement of said strings resulting from resonant conditions in said body and neck and substantially at right angles to the direction of movement of said strings resulting from playing of said strings whereby currents responsive to movement of said strings resulting from resonant conditions in said body and neck are substantially reduced.

4. An instrument according to claim 2, in which each string is positioned closer to one side of its associated strip than the other so that the generated magnetic flux lines cut the string at an angle to the plane of all of said strings.

References Cited by the Examiner UNITED STATES PATENTS 1,915,858 6/1933 Miessner 84--l.l6

ARTHUR GAUSS, Primary Examiner.

J. BUSCH, Assistant Examiner. 

1. IN A MUSICAL INSTRUMENT INCLUDING A BODY AND A PLURALITY OF STRINGS STRETCHED ACROSS A PORTION OF SAID BODY, MEANS FOR PROVIDING A PLURALITY OF INDIVIDUAL MAGNETIC FIELDS IN A GIVEN DIRECTION TRANSVERSE TO SAID STRINGS; AND ELECTRICAL PICKUP MEANS FOR SAID STRINGS FOR CONVERTING CURRENT INDUCED IN EACH STRING AS A CONSEQUENCE OF VIBRATIONAL MOVEMENT IN ITS ASSOCIATED MAGNETIC FIELD INTO AN ELECTRICAL SIGNAL OF MAGNITUDE AND FREQUENCY CONSTITUTING FUNCTIONS OF THE MAGNITUDE AND FREQUENCY OF VIBRATION OF SAID STRING, SAID MEANS FOR PROVIDING A PLURALITY OF MAGNETIC FIELDS COMPRISING A FLAT ELONGATED RECTANGULAR MEMBER OF MAGNETIC MATERIAL MADE UP OF ELONGATED PORTIONS IN THE FORM OF STRIPS MAGNETIZED SO THAT OPPOSITE SIDES CONSTITUTE NORTH AND SOUTH POLES, SAID STRIPS BEING POSITIONED AND EXTENDING BENEATH SAID STRINGS AND BEING OF A LENGTH GREATER THAN FIFTY PERCENT OF THE LENGTH OF SAID STRINGS. 